Method and a device for measuring a moisture content of granular inorganic material

ABSTRACT

In pelleting moist ore flour, for example, accurate measurement of moisture content of the sticky mass of material is necessary. This is effected by moving samples from the stream of material, piling them into a conical pile on a rotating table about 1 meter in diameter to form a pile having an inscribed spherical volume of about 30 cm radius, inserting a neutron-gamma ray-measuring probe into the center of the pile, making the measurement, removing the probe, and sweeping the pile from the table to enable repetition of said steps. Material adhering to the probe may be displaced therefrom as it is withdrawn from the pile. Suitable apparatus for so doing is also disclosed.

United States Patent [191 Beumer et al.

[ Mar. 26, 1974 METHOD AND A DEVICE FOR DX 5D 3 250/43 5 D X 250/435 D X 3,521,055 7/1970 Hirst et MEASURING A MOISTURE CONTENT OF 2; a j

, am et a GRANULAR INORGANIC MATERIAL 2,939,960 6/1960 Gunn Jansen, Aerdenhout; Herman all of Primary ExaminerArchie R. Borchelt Radstake, Uitgeest, Netherlands Attorney, Agent, or Firm-Hall & Houghton [73] Assignee: Koninklijke Nederlandsche Hoogovens En Staalfabieken N. V., ljmuiden, Netherlands Feb. 22, 1972 [22] Filed: In pelleting moist ore flour, for example, accurate Appl. No.: 228,090 measurement of moisture content of the sticky mass of material is necessary. This is effected by moving samples from the stream of material, piling them into a [30] Foreign Application Priority Data conical pile on a rotating table about 1 meter in diam- Feb. 25, i971 eter to form a having an inscribed spherical volume of about 30 cm radius, inserting a neutrongamma ray-measuring probe into the center of the pile, making the measurement, removing the probe, and sweeping the pile from the table to enable repetition of said steps. Material adhering to the probe may be displaced therefrom as it is withdrawn from the [56] References Cited UNITED STATES PATENTS pile. Suitable apparatus for so doing is also disclosed.

3,600,574 8/l97l Glaza et 250/435 D 7 Claims, 1 Drawing Figure METHOD AND A DEVICE FOR MEASURING A MOISTURE CONTENT OF GRANULAR INORGANIC MATERIAL The present invention relates to a method and a device for measuring the moisture content in a stream of granular inorganic material of fine grain size and having a strong tendency to stick together, f.i. a mixture of ore flour for the manufacture of iron ore pellets, in which the stream of material is sampled and a measuring probe is submerged into a sufficiently large sample said probe including sources for fast neutrons and for gamma-radiation, as well as detection means for slow neutrons and gamma-radiation.

A typical application of this method is found in the measuring of the moisture content in a moistened mixture of ore flour which is intended for the manufacture of ore pellets. Although in the further description the invention wil mainly be described with reference to this application the invention may also be applicable to advantage for measuring the moisture content in a stream of inorganic material of fine grain and strong tendency to stick together but of a different chemical composition and with another destination.

For charging blast-furnaces more and more use is made of ore pellets. These are manufactured from a mixture of fine-ground ore, a binding agent and water. For a good manufacture of ore pellets of high quality from such a mixture it is among others of the utmost importance that the moisture content is controlled very accurately. With a moisture content which, depending on the ore used and the binding agent used, is variable between 6 and 10 percent by weight of water, this moisture content should be controllable within an accuracy and within maximum deviations from a desired value of preferably less than 0.1 percent of water. 4

This moisture content in the ore mixture is obtained by adding the desired quantity of water to a massstream of dry ore flour. However, in doing this a good process is endangered by the possibility that the moistening device for metering the water shows disturbances or that something goes wrong with the measuring and control means used therewith. Also a drifting in the adjustment of this control means which may occur by contamination, to which such means are exposed in such very dusty processes, may give rise to disturbances in the process.

In the case of such a disturbance the moisture content in the mixture will deviate from the optimum and desired value, so that it becomes difficult to form ore pellets from this ore mixture or so that ore pellets of deviating quality are obtained.

Particularly in the latter case it will often become apparent only after considerable time lag that a correction of the moistening is necessary, but in the meantime an inadmissibly large quantity of material of unsuited quality will have been manufactured and used. Thereby the further manufacture of so called green (unbaked) pellets will be interrupted and hampered, so that a loss in production occurs which is very much higher than the said quantity of material of incorrect quality.

In view thereof it has appeared that there is the need fora measuring of the moisture content which is independent of the adequacy of operation of the moistening means. In fulfilling this need it is not sufficient to rely on a calculation of the moisture content of the basis of the measured streams of the ore mixture and the quantity of water supplied, but it is necessary to measure the moisture content in the mixture directly. For measuring the moisture content in granular materials several methods are known. One method which has been applied consists in the periodical sampling from the stream of the moistened ore mixture, after which this sample is weighed, dried and thereafter weighed again. In this way it is indeed possible to obtain an accurate measuring of the moisture content, but it is not possible in this way to obtain a rapid automatic determination of the moisture content. The drying requires a relatively long time, so that the result of the measurement only becomes available after a time lag which is inadmissibly long.

From the article of W. Kuhn Kontinuierliche eberwachung und Regelung des Feuchtgehaltes von Sintererzen nach den Neutronenstreuverfahren in the magazine Kerntechnik, Volume 5, no. 5, May 1963, pages 207 to 212, a method of the above given type is known for measuring the moisture content in sinter ore material. As compared with sinter material an ore flour mixture for manufacturing iron ore pellets has a much finer grain size and has much more tendency to stick together. This has as a result that application of the said known method and device will cause clogging or jamming in the device, or will give so much contamination that it is no more possible to obtain a reproduceable result of the measurement. This is a serious disadvantage, the more so because the measuring of the moisture content in the pellet material should be more accurate by an order of magnitude than is necessary for the measuring of the moisture content in sinter material. In the said known method a digging device digs material from a sinter material conveyor belt, which material is dumped into a cylinder, in which a measuring probe is submerged. At the lower end of the cylinder the material is continuously discharged with the aid of a discharging belt. For an ore flour mixture with its considerable sticking or clogging tendency as used for manufacturing ore pellets the discharging belt will withdraw the material from the cylinder quite irregularly or not at all, and even if the material is withdrawn there will be irregular flows along preferential patterns within the cylinder. Around the measuring probe the. clogging ore flour mixture will form a stagnant and mainly solid block, which has a very disadvantageous influence on the result of the measurement.

In view of the above the present invention provides a new method which makes it possible to give an accu rate measurement of the moisture content very rapidly in all conditions for such sticking inorganic materials.

In view thereof the invention proposes that periodically the sample is built up on a rotating table to form a conical heap having geometrically an inscribed sphere with a radius of at least 30 cm, into which thereupon the measuring probe is introduced in a manner known as such into the center and is kept therein during some time before it is withdrawn into a shielding structure, after which a new sample is formed.

In a manner similar to what has been described in the above given publication by Kuhn this method is based upon the selective deceleration of rapid neutrons by hydrogen atom nuclei. The rapid neutrons decelerated by the hydrogen in the moisture of the ore mixture are detected by the detector and the signals thus obtained are counted by the registration means and thereby form an indication for the quantity of hydrogen per unit of volume in the mixture. It is remarked in this respect that it has appeared in practice that in the usual ore mixtures as used for making pellets there is no more than a negligible variation in the quantity of hydrogen apart from variations in the quantity of hydrogen present in the water added to the mixture. The deviation in the measurement caused by the presence of other hydrogen, not present as water, appears to be well within the accuracy in which the moisture content should be controlled.

Moreover it is remarked that the result of the measurement obtained by counting signals caused by slow neutrons is also influenced by variations in density of the mixture. This gives the necessity to apply a correction to the signal measured, depending upon a measured value of the'density of the mixture. Therewith it is possible to correlate the measured quantity of moisture to the quantity by weight of the ore mixture, so that a measurement of percentage by weight is obtained. The measuring of the density necessary therewith is embodied with the aid of a source of) -radiation (gamma-radiation). The intensity of the 7 -radiation reflected by the material to be measured and absorbed thereby is a measure for the density of the material.

For a good measurement it is necessary to have the measuring probe entirely surrounded by the ore mixture, for which purpose it has appeared necessary to build the mixture to a layer first, into which it is possible to introduce the measuring probe in such a way that around the detector and the sources in all directions a quantity of material is present of at least 30 cm.

It is remarked that measuring probes for emitting rapid neutrons and of 7 -radiation as well as detectors for detecting slow neutrons and y -radiation are known as such. They are among others sold by the firm of Dr.Berthold, of Wildbad, Germany.

For realizing the new method the invention also relates to a device for measuring a moisture content. Such a device is in part of a type known as such including means for forming a sample from the material to be measured and a measuring probe containing sources for rapid neutrons and for y -radiation as well as detection means for slow neutrons and y -radiation. The improved device according to the invention includes a rotating table with driving means and a diameter of at least 1 m, a shovel for sampling, adapted to swing about a vertical axis, driving means therefor, said shovel being movable between a station for discharging the material in the main stream thereof for taking up the material in said station and a station above the rotating table to discharge this material onto the table, driving means for moving the measuring probe in a vertical direction above the rotating table between a position within a shielding structure and a zone at about 30 cm above the rotating table, as well as a shovel system adapted to make a sliding movement over the rotating table to remove the material from said table. It has appeared that with a device embodied in this way a sufficiently accurate measuring of the moisture content is possible, even in ore flour mixtures of very fine grain size and strong tendency of sticking together. In this respect it is remarked that the measuring probe in order to be suited for measuring the moisture content in such ore mixtures should be suited to measure in a range of 6 to percent by weight of water in the material, and

that this device should be able to measure the moisture content with an absolute accuracy better than 0.1 percent of water.

It is therewith also necessary to apply a correction for density variations between 1.7 and 2.3 metric tons per m. It has appeared that for such a measuring range a measuring probe is successfully applicable which has an americium-beryllium-source for fast neutrons of an intensity of preferably 100 millicurie, a cesium-137- source for 'y -radiation of an intensity of preferably 5 millicurie and a detector with preamplifier for catching slow neutrons and reflected 7 -radiation.

A source of inaccuracy in the measurement may consist in that the measuring probe during withdrawal from the heap of material to be measured draws part of this material from the heap, which material will stick to the probe, will dry and will thus remain in intimate contact therewith. This material would harmfully effect the result of a subsequent measurement. To avoid this it is preferred to apply, according to the invention, around the path of the measuring probe an annular doctoring or stripping member. This stripping member is preferably embodied as an opening for allowing the discharge of a jet directed in an inclined direction towards and onto the measuring probe. As a fluid for the jet it is possible to use air under pressure, but also to use water.

Care should be taken that there are provisions to avoid that the device will give undesired radiation to the environments. For this purpose the invention proposes as a preferred embodiment to have the means for moving the measuring probe include a weight or a spring drawing the measuring probe upwardly into the shielding structure if the energy supply to the driving means is interrupted, and that in the proximity of the rotating table there is a detector for 'y -radiation, adjusted to react on a too high intensity of the radiation. Such too high intensity may be the result of a too small quantity of material to be measured available on the rotating table, to which the detector will react by switching off the energization of the driving means. This latter possibility is for instance present if the electric energy supplied to the entire plant falls out, in cases in which such energy is used for moving the measuring probe. It is also possible, however, to detect with the aid of such a y -radiation meter whether an insufficient quantity of ore flour mixture is available around the probe. Also in that case the measuring probe will thus be withdrawn into the shielding structure.

The invention will now be explained with reference to the annexed drawing giving diagrammatically and by way of example only a device for measuring a moisture content according to the invention with the means for sampling etc. Reference numerals l and 2 indicate endless conveyor belts driven in the direction of the arrows and serving to convey a moistened ore flour mixture from a moistening device not shown to a device for forming ore pellets from the ore flour mixture in said stream. Said forming or moulding device also not being shown.

At the discharge end of belt 1, where the ore flour mixture is dumped onto conveyor 2, a sampling thief, spoon or blade 3 is provided, which is swingable about the center line of shaft 4. In one extreme ore flour this spoon or the like intercepts part of the oreflour material falling from conveyor belt 1, and in the other extreme position the spoon or the like 3 dumps this material onto a table 5. For this purpose in said latter extreme position there is a stationary doctor blade or shovel 6, which shovels the ore flour from the sampling spoon 3 when this spoon approaches this extreme position.

Table 5 is rotatable through transmission gear 7 by electric motor 8. A shovel 9 is movable over the table 5, said shovel being driven by a compressed air cylinder 10 so as to move between two extreme positions. The positioning of the doctor blade 6 and the table 5 with respect to each other are chosen in such a way that the material shoveled from the sampling spoon 3, in falling on the rotating table 5, forms a heap thereon in the shape of a frustum cone 11. In the axis of this cone a measuring probe and a shielding structure 13 are provided. The measuring probe is taken up in a shielding pipe 23. The shielding structure 13 contains paraffin oil or wax and lead. The measuring probe duct 12 contains a probe with an americium-beryllium-source of a strength of 100 millicurie, a cesium-l37-source of 5 millicurie and a detector with pre-amplifier, sensitive for slow neutrons and gamma-radiation. These elements of the measuring probe are not shown separately in the drawing as the structure of such a probe is known and obvious to the expert. It has neither been shown that the detector with preamplifier is connected to a postamplifier and registering or recording means. In the electronic circuit provisions are made in a manner known as such to use the signal of the reflected gammaradiation as a correction for the signal received from the slow neutrons. In this way a signal is obtained for the percentage of water in the ore mixture, which is corrected as to variations in density of the mixture. The electronic circuit is furthermore adapted or adjusted to operate in a measuring range of 61 0 percent by weight of water and a possible correction of density for densities varying between 1.7 and 2.3 metric tons per m It has appeared that for a time constant coefficient of 50 seconds such measuring apparatus gives a standard deviation as a result of the moisture content measurement of 0.049 percent and a standard deviation as a result of the density measurement of 0.0 1 8 percent, which gives a total standard deviation for the moisture content measurement of 0.052 percent of water. This deviation is acceptable for the accuracy with which the moisture content has to be measured.

The measuring probe is suspended to two cables 14 and 15, which extend over two pulleys l6 and 17 to two weights l8 and 19. Moreover the probe is connected to a piston 20 which is movable in a cylinder 21 for compressed air. By means of compressed air it is thus possible to push the measuring probe downwardly from the shielding structure 13 into the heap ll of ore material on the rotating table 5, and to be withdrawn therefrom again. The entire measuring device is positioned in a shielding cage not shown, so that it is possible to keep the quantity of radio-active radiation outside the cage below 0.25 mRem per hour. To the side of the heap 11 there is a gamma-radiation meter 22, shown diagrammatically. If this meter 22 detects gamma-radiation, the energization of the cylinder 20 is interrupted, so that the measuring probe 12 is retracted within the shielding structure 13 by the weights 18 and 19. The energization of cylinder 21 is also interrupted if the pressure of the compressed air drops too much or if the electric energy supply of the whole system falls out.

Motor 8 drives table 5 with a speed of about 2 to 3 revolutions per minute. After the sampling spoon 3 has dumped a sufficient quantity of material on table 5, so that the heap 11 has the desired frusto-conical shape with a height of at least cm, mechanical detectors not shown are energized thereby. In their turn these detectors stop the movement of the sampling spoon 3 and of the driving means for the rotating table 5. Thereupon cilinder 21 is energized, so that the measuring probe within the duct 12 is pushed downwardly into the heap 11. After finishing of the determination of the moisture content, the measuring probe in duct 12 is retracted within shielding structure 13 and rotating table 5 is emptied by means of the sliding shovel 9, which is slid over this rotating table by means of the compressed air cylinder 10. Thereupon a next measuring cycle can begin.

Below shielding structure 13 and above heap 11 there is a toroidal duct 23, to which a fluid such as air under pressure is supplied by duct 24. The duct 23 has orifices directed inwardly and downwardly to eject the air at high speed onto the outer shielding duct 12 of the probe in the direction of the arrows to loosen any ore sticking thereto. It is also possible to use water for this purpose, but in that case special measures should be taken to avoid this water from disturbing the correct measurement, e.g. by catching it after impinging on the probe and by leading it away from the heap of ore 11.

Of course modifications are possible, which however do not influence the general principle of the measurement as described. It has appeared that in the indicated way a sufficiently safe measuring of the moisture content is possible to check the good operation of the moistening means of the ore flour mixture, so that a highly reliable quality of this ore flour mixture and of the ore pellets formed therefrom is possible, while avoiding considerable losses of unsuitable material and energy.

We claim:

1. A method of measuring the moisture content in a stream of inorganic material of fine grain size having a strong tendency to stick together, for instance an ore flour mixture for manufacturing iron ore pellets, which comprises in combination as a measuring sequence:

a. forming a stream of the inorganic material,

b. periodically taking samples from said stream,

0. building on a rotating table a conical heap of said samples having an inscribed geometrical sphere with a radius of at least 30 cm.,

d. introducing a measuring probe into said heap to the center thereof, said measuring probe including sources of rapid neutrons and of 'y-radiation as well as detection-means for slow neutrons and y-radiation,

e. keeping the measuring probe in the conical heap during the time of measurement,

f. then withdrawing the probe into a shielding structure, and

g. finally wiping the conical heap from the rotating table, to enable the measuring sequence to be repeated.

2. A method as claimed in claim 1, wherein in step (f) as the probe is withdrawn from the conical heap, material adhering thereto is displaced from the probe and returned to the heap before the practice of step (g)- 3. Apparatus for measuring the moisture content of moist particulate material with the aid of a measuring probe including sources of rapid neutrons and of gamma radiation, adapted to be submerged in the ma terial, said apparatus comprising in combination:

a. means for forming a stream of the material,

b. a rotatable table having a diameter of at least one meter, said table being positioned proximate to said stream in spaced relation thereto,

c. a driving system connected to said table and operable for rotating the same,

(1. a sampling shovel movable between a sampling position intercepting said stream and a delivery position overlying said table,

e. measuring means including a measuring probe containing sources of rapid neutrons and gamma radiation as well as detection means for slow neutrons and gamma radiation, and a shielding means therefor,

f. means for mounting said measuring probe and shielding means above said table for movement of said probe between a retracted position within said shielding means and a measuring position about 30 centimeters above the center of said table, means for operating said sampling shovel while said table is being rotated for taking samples from said stream and delivering them to said rotating table for forming a conical pile of the material centered on said table and having an inscribed spherical volume of at least 30 centimeters radius,

h. means for operating said mounting means for moving said probe to said measuring position in the so formed conical pile of material, for affecting a measurement of the moisture content thereof, and for thereafter moving said probe to said retracted position, and

i. means positioned to move across said table to clear the same of said piled material.

4. Apparatus as claimed in claim 3, which further comprises:

j. stripping means embracing the path of movement of said probe between said measuring and retracted positions for stripping from said probe material adhered thereto when said probe is retracted.

5. Apparatus as claimed in claim 3, wherein said stripping means comprises means for delivering stripping fluid in an inclined direction against said measuring probe.

6. Apparatus as claimed in claim 3, wherein said operating means (h) further comprises:

j. means biasing said probe to move to its retracted position, and

k. power driven means for moving said probe to its measuring position against the forces of said biasing means,

so that on interruption of the power to said power driven means, said biasing means retracts said probe.

7. Apparatus as claimed in claim 6, further comprising a gamma radiation detector positioned close to said table to detect gamma radiation emanating from said pile of material, and means responsive to the detection thereby of radiation in excess of a predetermined quantity for effecting retraction of said probe. 

1. A method of measuring the moisture content in a stream of inorganic material of fine grain size having a strong tendency to stick together, for instance an ore flour mixture for manufacturing iron ore pellets, which comprises in combination as a measuring sequence: a. forming a stream of the inorganic material, b. periodically taking samples from said stream, c. building on a rotating table a conical heap of said samples having an inscribed geometrical sphere with a radius of at least 30 cm., d. introducing a measuring probe into said heap to the center thereof, said measuring probe including sources of rapid neutrons and of gamma -radiation as well as detection means for slow neutrons and gamma -radiation, e. keeping the measuring probe in the conical heap during the time of measurement, f. then withdrawing the probe into a shielding structure, and g. finally wiping the conical heap from the rotating table, to enable the measuring sequence to be repeated.
 2. A method as claimed in claim 1, wherein in step (f) as the probe is withdrawn from the conical heap, material adhering thereto is displaced from the probe and returned to the heap before the practice of step (g).
 3. Apparatus for measuring the moisture content of moist particulate material with the aid of a measuring probe including sources of rapid neutrons and of gamma radiation, adapted to be submerged in the material, said apparatus comprising in combination: a. means for forming a stream of the material, b. a rotatable table having a diameter of at least one meter, said table being positioned proximate to said stream in spaced relation thereto, c. a driving system connected to said table and operable for rotating the same, d. a sampling shovel movable between a sampling position intercepting said stream and a delivery position overlying said table, e. measuring means including a measuring probe containing sources of rapid neutrons and gamma radiation as well as detection means for slow neutrons and gamma radiation, and a shielding means therefor, f. means for mounting said measuring probe and shielding means above said table for movement of said probe between a retracted position within said shielding means and a measuring position about 30 centimeters above the center of said table, f. means for operating said sampling shovel while said table is being rotated for taking samples from said stream and delivering them to said rotating table for forming a conical pile of the material centered on said table and having an inscribed spherical volume of at least 30 centimeters radius, h. means for operating said mounting means for moving said probe to said measuring position in the so formed conical pile of material, for affecting a measurement of the moisture content thereof, and for thereafter moving said probe to said retracted position, and i. means positioned to move across said table to clear the same of said piled material.
 4. Apparatus as claimed in claim 3, which further comprises: j. stripping means embracing the path of movement of said probe between said measuring and retracted positions for stripping from said probe material adhered thereto when said probe is retracted.
 5. Apparatus as claimed in claim 3, wherein said stripping means comprises means for delivering stripping fluid in an inclined direction against said measuring probe.
 6. Apparatus as claimed in claim 3, wherein said operating means (h) further comprises: j. means biasing said probe to move to its retracted position, and k. power driven means for moving said probe to its measuring position against the forces of said biasing means, so that on interruption of the power to said power driven means, said biasing means retracts said probe.
 7. Apparatus as claimed in claim 6, further comprising a gamma radiation detector positioned close to said table to detect gamma radiation emanating from said pile of material, and means responsive to the detection thereby of radiation in excess of a predetermined quantity for effecting retraction of said probe. 